Method for producing sol-gel compositions with a reduced solvent content and improved storage properties, and the use thereof

ABSTRACT

The present invention relates to a process for producing inorganic or organic-inorganic (hybrid) materials by hydrolysis and condensation of mono- or low molecular alkoxides and their use for coating surfaces and modifying organic polymers.

[0001] The present invention relates to a process for producinginorganic or organic-inorganic (hybrid) materials by hydrolysis andcondensation of mono- or low molecular alkoxides and their use forcoating surfaces and modifying organic polymers.

[0002] Alkoxides, generally (organo-)silicon alkoxides areconventionally used in sol-gel reactions and are reacted in a solventwith water in the presence of a catalyst to produce suitable coatingformulations. After a certain reaction time, the reaction solution isapplied to the desired surface and after evaporation of the volatilecomponents is finally cured by heat or radiation. The usually highlycrosslinked sol-gel coatings obtained in this way are generallytransparent, outstandingly resistant to solvents and chemicals andwear-resistant.

[0003] A fundamental problem of sol-gel reactive solutions is that thequantity of solvent can only be reduced to a very limited extent andtherefore the solids content can be increased without the pot lifebecoming too short. This applies in particular to systems in which,during production, the alcohols conventionally used as solvents stronglyinfluence the reaction kinetics of the condensation andtransesterification of the alkoxides used. Owing to the alcoholsliberated during condensation of alkoxides to siloxanes, the solventcontent additionally increases, as during condensation of, for example,tetraethyl orthosilicate 72 wt. % of ethanol are theoreticallyliberated.

[0004] Alkoxides and silanols based on cyclic carbosiloxanes areparticularly suitable for producing organic-inorganic hybrid materials,as described for example in WO 94/06807, EP-A-0 787 734 and EP-A-0 947520. A substantial disadvantage of the sol-gel solutions describedthere, however, is their high solvent content and the limited pot life.Solvent contents greater than 70 wt. % are no longer acceptable in thepaint industry on ecological grounds, in particular in sectors where thedisposal of the solvent cannot be handled correctly.

[0005] WO 98/52992 describes oligomers of the above-mentioned cycliccarbosiloxanes which can be co-condensated with alkoxides and/ornanoparticles in a solvent in the presence of a catalyst and water. Theproduction of such condensates corresponds to that described, forexample, in DE-A-196 03 242 and in WO 94/06897, wherein only low solidscontents could be achieved.

[0006] The object of the present invention was therefore to providesol-gel compositions based on cyclic carbosiloxanes with a solventcontent of less than 60 wt. % and a pot life of at least 7 days.

[0007] The present invention relates to a process for producing sol-gelcompositions from cyclic carbosiloxanes and (organo-)metallic alkoxideswith a solvent content less than 60 wt. % and a stability in storage ofat least 7 days, characterised in that the process steps

[0008] A) reaction of a mixture containing cyclic carbosiloxanes and(organo-)metallic alkoxides with water in the presence of a catalyst andoptionally additional solvent, and

[0009] B) partial or complete removal of the alcohols liberated duringhydrolysis and condensation and of the optionally added solvent

[0010] are carried out in succession.

[0011] In a preferred embodiment of the process according to theinvention, the sol-gel compositions are produced by the successiveprocess steps

[0012] A)

[0013] a) reaction of the cyclic carbosiloxanes with water in thepresence of a catalyst and optionally additional solvent,

[0014] then

[0015] b) addition of the (organo-)metallic alkoxide, and

[0016] B) partial or complete removal of the alcohols liberated duringhydrolysis and condensation and of the optionally added solvent.

[0017] The sol-gel compositions produced according to the inventionpreferably contain less than 50 wt. %, particularly preferably less than40 wt. % of solvent. They are stable in storage for at least 7 days(i.e. the sol-gel compositions have not gelled), but are condensed tothe extent that curing after application to a surface can take, e.g.,place without further addition of components (for example water,catalysts).

[0018] Cyclic carbosiloxanes in the context of the invention are thoseof Formula (I)

[0019] in which

[0020] R¹ represents C₁ to C₄ alkyl,

[0021] R² represents hydrogen and/or C₁ to C₄ alkyl

[0022] a is the integer 0, 1 or 2,

[0023] n is the integer 2 to 10 and

[0024] m is the integer 3 to 5.

[0025] Oligomeric cyclic carbosiloxanes of Formula (I) and theirproduction are described in WO 98/52992 and can be used as well in theprocedure described.

[0026] According to the invention, (organo-)silicon alkoxides of Formula(II)

R³ _(b)Si(OR⁴)_(4-b)  (II),

[0027] are preferred as (organo-)metallic alkoxides, in which

[0028] R³ represents a C₁ to C₄ alkyl or C₆ to C₁₀ aryl radical

[0029] R⁴ represents a C₁ to C₄ alkyl radical and

[0030] b is an integer 0, 1 or 2.

[0031] Tetraethoxysilane is particularly preferably used as siliconalkoxide of Formula (II).

[0032] Water in the molar ratio 1:2 to 3:1, preferably 3:1 to 1.5:1, isused for hydrolysis of the alkoxy groups Si—O—R.

[0033] 1 to 90, preferably 25 to 60 wt. % of the cyclic carbosiloxaneand 99 to 20, preferably 75 to 40 wt. % of the (organo-)metallicalkoxide are used to produce the sol-gel compositions according to theinvention.

[0034] Aqueous inorganic or organic acids or bases such as formic acid,p-toluene sulphonic acid, hydrochloric acid or sodium and potassiumhydroxide or organic metal compounds are mentioned as examples ofcatalysts. The catalyst is preferably an acid, particularly preferablypara-toluene sulphonic acid.

[0035] Between 0.01 wt. % and 5 wt. % are preferably added as catalystbased on the reaction mixture.

[0036] Suitable solvents are those with a boiling point higher than 80°C., for example 1-butanol, 1-pentanol, 2-pentanol, 1-methoxy-2-propanolor diacetone alcohol.

[0037] The alcohols liberated during hydrolysis and condensation and theoptionally added solvent are removed by distillation, preferably undernormal pressure.

[0038] The process according to the invention for producing sol-gelcompositions also allows the substitution of protic solvents, such asalcohols, by aprotic solvents such as ketones, esters or ethers. Asaprotic solvents do not react with isocyanates for example, mixtures ofsol-gel compositions produced in this way can be obtained withisocyanate group-containing and OH group-containing polymers without theblocked isocyanates described in WO 98/38251 having to be used toproduce such organic-inorganic hybrid materials. Inorganically modifiedpolyurethanes which can be used as coatings with improved wearresistance can be obtained from these mixtures.

[0039] Additives such as flow-control agents or wetting agents can beadded to the sol-gel compositions produced according to the inventionbefore, during or after production in order to improve, for example, theappearance of the film. The sol-gel coatings can be coloured by addingorganic or inorganic dyes (soluble) or pigments (insoluble). Theaddition of UV protective agents primarily serves to protect the coatedsubstrate, for example plastics material.

[0040] By adding nanoparticles to the sol-gel compositions producedaccording to the invention, the mechanical properties, for example, ofthe coatings which can be produced therefrom can also be improved.Examples of suitable preparations of nanoparticles are dispersions ofSiO₂, Al₂O₃— or TiO₂— containing particles in water or solvents. Inorder to be able to produce transparent coatings, the particle size ofthe nanoparticles is preferably less than 100 nm, particularlypreferably less than 50 nm (determined by ultracentrifuging).

[0041] The invention also relates to the sol-gel compositions producedaccording to the invention for producing coatings for use, for exampleon glass, ceramics, metals and plastics materials.

[0042] Application can be by any common painting technique such asspraying, dipping, centrifuging, casting, flow coating or painting.

[0043] After application, curing can take place at ambient temperatureor can be forced at higher temperatures.

[0044] The invention also relates to the use of the sol-gel compositionsproduced according to the invention for inorganic modification oforganic polymers. Examples of organic polymers are polyethers,polyesters, polyvinyl alcohols, polycarbonates or copolymers andmixtures (blends) thereof. Hydroxyl group-containing organic polymers(such as polyols) can be modified particularly well with the sol-gelcompositions as compatibility therewith is generally very good.

[0045] Modification of epoxides or polyurethanes by the sol-gelcompositions produced according to the invention leads, for example, tocoatings with clearly improved wear resistance.

EXAMPLES

[0046] D4-diethoxide oligomer, an oligomer mixture of partiallycondensed cyclo-{SiO[(CH₂)₂SiCH₃(OEt)₂]}₄ was produced as described inWO 98/52992. Tetraethyl orthosilicate (TEOS) and the solvents used wereused without further purification. A 0.1 N aqueous solution of p-toluenesulphonic acid (p-TSS solution) was used as a catalyst for condensationand hydrolysis. Levasil® 200S/30 (Bayer AG, Leverkusen) is a 30%colloidal dispersion of amorphous SiO₂ nanoparticles (primary particlesize approximately 15 nm) which is cationically stabilised at pH=3.8.

[0047] The calculated solids contents given are based on the solidstheoretically remaining after complete hydrolysis and condensation ofthe alkoxides contained in the sol-gel reaction solution and completeremoval of the volatile components.

[0048] The solids contents were determined experimentally by weighing in1 g of the sol-gel reaction solution into a crystallisation basin(diameter: 7.5 cm) and evaporating the volatile components at 130° C. ina circulating air oven for 1 hour.

[0049] The stability in storage of the sol-gel compositions producedaccording to the invention was tested (gelling) by allowing them tostand at ambient temperature and at 50° C. in a well-sealed test tubefor at least 14 days.

[0050] All percentages are based on the weight.

Example 1 Sol-gel Composition (52 %) in 1-methoxy-2-propanol

[0051] 8.2 g p-TSS solution were added to 25 g D4-diethoxide oligomer in50 g 1-methoxy-2-propanol while stirring. After stirring for 30 minutesat ambient temperature 47.2 g TEOS were added. The reaction mixture wasthen heated for 1 hour to 50° C. (internal thermometer). Finally, thetemperature was increased (maximum bath temperature 110° C.) until 40.3g of volatile constituents with a boiling temperature <90° C. (primarilythe ethanol formed) could be distilled off. After cooling, the sol-gelcomposition was obtained as a low viscosity, clear liquid.

[0052] Experimental solids content: 52%

[0053] Stability in storage (ambient temperature): 41 days

[0054] Stability in storage (50° C.): 8 days.

Example 2 Sol-gel Composition (73%) in 1-methoxy-2-propanol

[0055] 8.2 g p-TSS solution were added to 25 g D4-diethoxide oligomer in50 g 1-methoxy-2-propanol while stirring. After stirring for 30 minutesat ambient temperature 47.2 g TEOS were added. The reaction mixture wasthen heated for 1 hour to 50° C. (internal thermometer). Finally, thetemperature was initially increased such that, as in Example 1, 42.9 gof volatile constituents with a boiling temperature <90° C. (primarilythe ethanol formed) could be distilled off. The temperature was thenincreased further (maximum bath temperature 130° C.), so a further 15.3g of volatile constituents with a boiling temperature <100° C. could becondensed off. After cooling, the sol-gel composition was obtained as aviscous, clear liquid.

[0056] Experimental solids content: 73%

[0057] Stability in storage (ambient temperature): 13 days

[0058] Stability in storage (50° C.): 4 days.

Example 3 Sol-gel Composition (57%) in 1-butanol

[0059] The process was carried out as described in Example 1, using1-butanol instead of 1-methoxy-2-propanol as solvent. Distillationproduced 42.7 g of volatile constituents.

[0060] Experimental solids content: 57%

[0061] Stability in storage (ambient temperature): 31 days

[0062] Stability in storage (50° C.): 10 days.

Example 4 Sol-gel Composition (61%) in 1-pentanol

[0063] The process was carried out as described in Example 1, using1-pentanol instead of 1-methoxy-2-propanol as solvent. Distillationproduced 40.9 g of volatile constituents.

[0064] Experimental solids content: 61%

[0065] Stability in storage (ambient temperature): 39 days

[0066] Stability in storage (50° C.): 10 days.

Example 5 Sol-gel Composition (40%) in methoxypropylacetate

[0067] 8.2 g p-TSS solution were added to 25 g D4-diethoxide oligomer in50 g methoxypropylacetate while stirring. After stirring for 30 minutesat ambient temperature 47.2 g TEOS were added, and the solution becamecloudy. The reaction mixture was then heated for 2 hours to 50° C.(internal thermometer) and 10 ml 2-methyl ethyl ketone were then added.After cooling to ambient temperature, filtration from slightlycolourless precipitate was carried out. Finally, 35.5 g of volatileconstituents with a boiling temperature <90° C. (primarily the ethanolformed) were distilled off from the clear filtrate obtained (127.1 g) ata maximum bath temperature of 110° C. After cooling, the sol-gelformulation was obtained as a low viscosity, clear liquid.

[0068] Experimental solids content: 40%

[0069] Stability in storage (ambient temperature): 15 days

[0070] Stability in storage (50° C.): 3 days.

Example 6 Sol-gel Composition (41%) in n-butylacetate

[0071] 8.2 g p-TSS solution were added to 25 g D4-diethoxide oligomer in50 g n-butylacetate while stirring. After stirring for 30 minutes atambient temperature 47.2 g TEOS were added and the cloudy reactionmixture was then heated for 2 hours to 50° C. (internal thermometer).After cooling to ambient temperature, filtration from slightlycolourless precipitate was carried out. Finally, 35.5 g of volatileconstituents with a boiling temperature <90° C. (primarily the ethanolformed) were distilled off from the clear filtrate obtained (117.7 g) ata maximum bath temperature of 110° C. After cooling, the sol-gelcomposition was obtained as a low viscosity, clear liquid.

[0072] Experimental solids content: 41.5%

[0073] Stability in storage (ambient temperature): 28 days

[0074] Stability in storage (50° C.): 7 days.

Example 7 Sol-gel Composition (53%) in 1-methoxy-2-propanol

[0075] 8.2 g p-TSS solution were added to 25 g D4-diethoxide oligomer in50 g 1-methoxy-2-propanol while stirring. After stirring for 30 minutesat ambient temperature 47.2 g TEOS were added. The reaction mixture wasthen heated for 1 hour to 50° C. (internal thermometer). After adding0.1 g NaHCO₃, the temperature was then increased (maximum bathtemperature 110° C.) until 40.4 g of volatile constituents with aboiling temperature <90° C. (primarily the ethanol formed) could bedistilled off. After cooling, the sol-gel composition was obtained as alow viscosity, clear liquid.

[0076] Experimental solids content: 53%

[0077] Stability in storage (ambient temperature): 8 days

[0078] Stability in storage (50° C.): 1 day.

Example 8 Sol-gel Composition (44%) in methoxypropylacetate

[0079] 8.2 g p-TSS solution were added to 25 g D4-diethoxide oligomer in50 g methoxypropylacetate and stirring. After stirring for 30 minutes atambient temperature 47.2 g TEOS were added, and the solution becamecloudy. The reaction mixture was then heated for 1 hour to 50° C.(internal thermometer). Finally, 40.1 g of volatile constituents with aboiling temperature <90° C. (primarily the ethanol formed) was distilledoff after addition of 0.1 g NaHCO₃, at a maximum bath temperature of110° C. After cooling, the sol-gel composition was obtained as a lowviscosity, clear liquid.

[0080] Experimental solids content: 44.0%

[0081] Stability in storage (ambient temperature): 23 days

[0082] Stability in storage (50° C.): 1 day.

Example 9 Sol-gel Composition (50%) in 1-methoxy-2-propanol

[0083] 8.1 g p-TSS solution were added to 25 g D4-diethoxide oligomer in50 g 1-methoxy-2-propanol while stirring. After stirring for 30 minutesat ambient temperature 47.2 g TEOS were added and stirring was continuedfor 30 minutes. A further 2.1 g p-TSS solution were then added and thereaction mixture was stirred for 80 minutes at ambient temperature andthen heated for 1 hour to 50° C. (internal thermometer). Subsequently,45.8 g of volatile constituents with a boiling temperature <90° C.(primarily the ethanol formed) were distilled off at a maximum bathtemperature of 110° C. After cooling, 83.9 g of the sol-gel compositionwere obtained as a low viscosity, clear liquid.

[0084] Experimental solids content: 50.0%

[0085] Stability in storage (ambient temperature): 7 days.

Example 10 Sol-gel Composition (55%) in 1-methoxy-2-propanol withSiO₂-nanoparticles

[0086] 8.75 g p-TSS solution were added to a mixture of 102 g of TEOSand 25 g ethanol while stirring and the reaction mixture was stirred for1 hour. 12.5 g Levasil 200S/30 (previously adjusted to pH=2 by addingconcentrated hydrochloric acid) dissolved in 6 ml ethanol were thenadded with vigorous stirring and the reaction mixture was stirred for 30minutes. 77.1 g of the TEOS-nano-SiO₂ condensate obtained in this waywere then mixed with 30 g D4-diethoxide oligomer and 45 g1-methoxy-2-propanol and heated for 1 hour to 50° C. 59.9 g of volatileconstituents were then distilled off at a bath temperature <110° C.After cooling, 89.4 g of the sol-gel composition were obtained as lowviscosity, clear liquid.

[0087] Experimental solids content: 55%

[0088] Stability in storage (ambient temperature): 31 days

[0089] Stability in storage (50° C.): 10 days.

1. Process for producing sol-gel compositions from cyclic carbosiloxanesand (organo-)metallic alkoxides with a solvent content less than 60 wt.% and a stability in storage of at least 7 days, characterised in thatthe process steps A) reacting a mixture containing cyclic carbosiloxanesand (organo-)-metallic alkoxides with water in the presence of acatalyst and optionally additional solvent, and B) partial or completeremoval of the alcohols liberated during hydrolysis and condensation andof the optionally added solvents are carried out in succession. 2.Process according to claim 1, characterised in that the process step A)consists of a) reacting the cyclic carbosiloxanes with water in thepresence of a catalyst and optionally additional solvent, and subsequentb) addition of the (organo-)metallic alkoxide.
 3. Process according toclaim 1, characterised in that the sol-gel compositions contain lessthan 50 wt. % of solvent.
 4. Process according to claim 1, characterisedin that the sol-gel compositions contain less than 40 wt. % of solvent.5. Process according to claim 1, characterised in that cycliccarbosiloxanes of Formula (I), wherein

R¹ represents C₁ to C₄ alkyl, R² represents hydrogen and/or C₁ to C₄alkyl a is the integer 0, 1 or 2, n is the integer 2 to 10 and m is theinteger 3 to 5 are used.
 6. Process according to claim 1, characterisedin that (organo-)metallic oxides of Formula (II) R³_(b)Si(OR⁴)_(4-b)  (II), wherein R³ represents a C₁ to C₄ alkyl or C₆ toC₁₀ aryl radical R⁴ represents a C₁ to C₄ alkyl radical and b is aninteger 0, 1 or 2 are used.
 7. Process according to claim 4,characterised in that tetraethoxysilane is used as (organo-)metallicoxide.
 8. Process according to claim 1, characterised in that aqueousinorganic or organic acids are used as catalysts.
 9. Use of sol-gelformulations according to claims 1 to 6 to produce coatings.
 10. Use ofsol-gel formulations according to claims 1 to 6 to modify organicpolymers.